1. Field of the Invention
The present invention relates to a toner for use in electrophotography. In addition, the present invention also relates to a fixing method and an image forming method using the toner.
2. Discussion of the Background
When a toner image formed by an electrophotographic image forming method is fixed, heat roller fixing methods are typically used. In heat roller fixing methods, a toner image is contacted with a heat roller upon application of pressure to be heated and melted. Therefore, the heat roller fixing methods tend to cause an offset problem in that part of a fused toner image is adhered and transferred to the surface of the heat roller, and then the part of the toner image is re-transferred to an undesired portion of the sheet itself or the following sheet of a recording material. In attempting to prevent occurrence of the offset problem, a technique in which a fixing oil such as a silicon oil is applied or penetrated to the heat roller is proposed. On the other hand, the heat roller fixing methods tend to cause another problem in that a recording material having a toner image thereon winds around a heat roller (this phenomenon is hereinafter referred to as a winding problem). In attempting to prevent occurrence of the winding problem, a technique in which a separation mechanism (such as a separation pick and a separation plate) configured to separate the recording material and the heat roller is arranged on the heat roller is proposed.
However, in order to downsize image forming apparatus, oilless fixing devices without a fixing oil applying system have been typically used. In this case, the toner adhered to the heat roller tends to damage the separation mechanism, and as a result, the recording material cannot be well separated from the heat roller.
In attempting to solve these problems, a technique in which a wax (such as polypropylene and polyethylene) is included in a toner to improve the ability of the toner to separate a toner image from a fixing member such as a heat roller (this ability is hereinafter referred to as separativeness) and releasability of the toner itself is proposed. However, a wax having relatively low polarity cannot be well dispersed in a polyester resin having relatively high polarity, which is typically used in toners.
In attempting to solve this problem, modified waxes such as oxidized polyolefin waxes having a polar group on the end thereof have been used. Such waxes can be well dispersed in polyester resins. However, since modified waxes typically have relatively high viscosity compared to unmodified waxes, such waxes cannot function as a release agent, i.e., a toner including such a wax has low releasability, separativeness and hot offset resistance.
On the other hand, a technique in which the surface of a heat roller is covered with materials having good releasability (such as fluorocarbon resins) is proposed. However, such a heat roller has poor reproducibility and durability.
It is relatively difficult to improve hot offset resistance and separativeness of full color toners compared to cases using monochrome toners. This is because the viscosity of full color toners is decreased so that the surface of a full color toner image is smoothened to some extent to obtain a brilliant full color image having good glossiness, transparency and color reproducibility. However, such a toner having low viscosity tends to adhere to a heat roller when the toner is heat-melted, due to deterioration of the intermolecular cohesive force thereof. It is possible to improve separativeness and hot offset resistance by increasing elasticity of the toner, but the produced image has poor glossiness. It is difficult for full color toners to produce high quality images while having good fixability.
In attempting to solve these problems, Japanese patent No. 3458629 discloses a toner including wax particles having, a particle diameter of less than 1 μm in an amount of from 55 to 95% by number based on the total number of wax particles. However, since wax particles having a particle diameter of less than 1 μm tend not to immediately exude to the surface of the toner particles, such a toner has poor separativeness.
Published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2004-126268 discloses a toner including a wax having a particle diameter distribution property such that a top peak is present in a particle diameter range of from 1.0 to 1.5 μm, wherein wax particles having a particle diameter of not less than 1.0 μm and less than 1.5 μm are included in the toner in an amount of not less than 20% by number and less than 40% by number. In this case, especially when the toner is used in a one-component developer, a problem in that the toner tends to firmly adhere to a developing blade or a photoreceptor is caused.
These techniques are still insufficient to provide a toner having a good combination of oilless fixability, developability, and cleanability.